Ascending colon

At a glance

English

Ascending colon

Latin (TA2)

Colon ascendens

System

Digestive

Region

Abdomen

Side

Single, on the midline

About the ascending colon

The ascending colon runs upwards from the caecum, at the level of the ileocaecal valve, to the right colic (hepatic) flexure beneath the right lobe of the liver, a length of about 12 to 15 cm. There it turns sharply forwards and to the left to become the transverse colon. It is narrower than the caecum and lies in the right flank, in the right lumbar region of the abdomen.

It is normally retroperitoneal: peritoneum covers its front and sides, but its back is fused to the posterior abdominal wall, where it rests on the iliacus, quadratus lumborum and the lower part of the right kidney. A gutter of peritoneum on its outer side, the right paracolic gutter, can carry fluid or pus between the upper abdomen and the pelvis. In front lie coils of small intestine, the greater omentum and the front abdominal wall. In some people a short mesentery remains, making it unusually mobile.

Like the rest of the colon it shows three typical external features. Its outer longitudinal muscle is gathered into three flat bands, the taeniae coli, which are shorter than the bowel and so pucker the wall into a series of pouches, the haustra. Small tags of fat covered with peritoneum, the omental appendices, hang from its surface. Inside, crescent-shaped semilunar folds mark the boundaries between haustra. The lining has no villi but deep crypts with many mucus-secreting goblet cells.

The ascending colon receives liquid contents from the ileum and begins the main work of the large bowel: absorbing water and salts so that the contents thicken. Its embryological origin from the midgut explains its supply from the superior mesenteric artery and why pain from it is felt around the navel. Cancers on the right side of the colon often grow large without blocking the wide lumen, and may first show as anaemia from slow bleeding. In a right hemicolectomy this segment is removed with the caecum and part of the transverse colon.

Function and supply

Function

Absorbs water and electrolytes from the liquid contents arriving from the ileum and moves them on towards the transverse colon.

Nerve supply

Parasympathetic fibres from the vagus and sympathetic fibres from the superior mesenteric plexus.

Blood supply

The ileocolic and right colic arteries from the superior mesenteric artery, linked by the marginal artery; veins drain to the superior mesenteric vein.